﻿#region Using

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;
using System.Net;

#endregion

namespace BlogEngine.Core.Ping
{
    /// <summary>
    /// Manages to send out trackbacks and then pingbacks if trackbacks aren't supported by the linked site.
    /// </summary>
    public static class Manager
    {
        /// <summary>
        /// Sends the trackback or pingback message.
        /// <remarks>
        /// It will try to send a trackback message first, and if the refered web page
        /// doesn't support trackbacks, a pingback is sent.
        /// </remarks>
        /// </summary>
        public static void Send(IPublishable item, Uri itemUrl)
        {
            foreach (Uri url in GetUrlsFromContent(item.Content))
            {
                string pageContent = ReadFromWeb(url);
                Uri trackbackUrl = GetTrackBackUrlFromPage(pageContent);
                bool isTrackbackSent = false;

                if (trackbackUrl != null)
                {
                    TrackbackMessage message = new TrackbackMessage(item, trackbackUrl, itemUrl);
                    isTrackbackSent = Trackback.Send(message);
                }

                if (!isTrackbackSent)
                {
                    Pingback.Send(itemUrl, url);
                }
            }
        }

        #region "RegEx Methods"

        /// <summary>
        /// Regex used to find all hyperlinks.
        /// </summary>
        //private static readonly Regex urlsRegex = new Regex(@"\<a\s+href=""(http://.*?)"".*\>.+\<\/a\>", RegexOptions.IgnoreCase | RegexOptions.Compiled);
        private static readonly Regex urlsRegex = new Regex(@"<a[^(href)]?href=""([^""]+)""[^>]?>([^<]+)</a>", RegexOptions.IgnoreCase | RegexOptions.Compiled);

        /// <summary>
        /// Regex used to find the trackback link on a remote web page.
        /// </summary>
        private static readonly Regex trackbackLinkRegex = new Regex("trackback:ping=\"([^\"]+)\"", RegexOptions.IgnoreCase | RegexOptions.Compiled);

        /// <summary>
        /// Gets all the URLs from the specified string.
        /// </summary>
        private static List<Uri> GetUrlsFromContent(string content)
        {
            List<Uri> urlsList = new List<Uri>();
            foreach (Match myMatch in urlsRegex.Matches(content))
            {
                string url = myMatch.Groups[1].ToString().Trim();
                Uri uri;
                if (Uri.TryCreate(url, UriKind.Absolute, out uri))
                    urlsList.Add(uri);
            }

            return urlsList;
        }

        /// <summary>
        /// Examines the web page source code to retrieve the trackback link from the RDF.
        /// </summary>
        private static Uri GetTrackBackUrlFromPage(string input)
        {
            string url = trackbackLinkRegex.Match(input).Groups[1].ToString().Trim();
            Uri uri;

            if (Uri.TryCreate(url, UriKind.Absolute, out uri))
                return uri;
            else
                return null;
        }

        #endregion

        /// <summary>
        /// Returns the HTML code of a given URL.
        /// </summary>
        /// <param name="sourceUrl">The URL you want to extract the html code.</param>
        /// <returns></returns>
        private static string ReadFromWeb(Uri sourceUrl)
        {
            string html;
            using (WebClient client = new WebClient())
            {
                client.Headers.Add("User-Agent", "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0)");
                html = client.DownloadString(sourceUrl);
            }
            return html;
        }
    }
}
